This invention relates generally to radio transmitters, and more specifically to a multichannel radio transmitter incorporating a phase-locked loop (PLL) frequency synthesizer for production of various transmitting frequencies. The transmitter according to the invention is particularly well adaptable for a multichannel transceiver.
The PLL frequency synthesizer has recently found its way into multichannel transceivers. combined with a single reference frequency oscillator, the synthesizer provides a choice of a number of different frequencies required for multichannel transmission and multichannel superheterodyne reception. Advantageously, the PLL frequency synthesizer drastically reduces the number of quartz crystal units in crystal oscillators used in the transceiver and is further capable of providing a carrier of highly stabilized frequency.
The mulichannel transmitter with the PLL frequency synthesizer has a serious drawback, however. The synthesizer inevitably generates some spurious frequency signal for some brief time immediately after switching from one transmission channel to another, or in the event of the malfunctioning of some of its components. Such spurious signal generation by the sysnthesizer results in wave radiation into space at other than the prescribed frequencies and, possibly, in the damage of the output stage of the transmitter.